1. Field of the Invention
The present invention is generally related to wireless communications and more particularly related to a scalable medium access control (“MAC”) module for use in multi-hop wireless network communications over high bandwidth wireless communication channels based on ultra-wide band (“UWB”) or orthogonal frequency division multiplexing (“OFDM”) among others.
2. Related Art
In recent times, UWB technology has gone through significant progress. Many different competing proposals for UWB networking have been consolidated into two major camps. The first proposal falls under the WiMedia umbrella and is backed by companies including Intel, Microsoft, and Phillips, among others. The second proposal falls under the UWB Forum umbrella and is backed by Motorola, Freescale, among other companies.
UWB communication technologies hold out the promise of high speed transmission rates over short distances. However, to extend the coverage of UWB networks without compromising the high speed transmission rates, a wireless mesh network is needed. Additionally, by using mesh networking to extend UWB coverage, the network reliability and fault tolerance of UWB networks can advantageously be improved.
The conventional medium access control (“MAC”) protocols of UWB networks, in particular, IEEE 802.15.3 MAC and WiMedia MAC (including the multi-band OFDM alliance (“MBOA”) MAC) can also support mesh networking, the performance of these conventional MAC solutions lacks scalability in a multi-hop mesh network environment.
Additionally, no single UWB communication solution has taken hold in the industry. For example, the physical layer of WiMedia is based on the MBOA (“MBOA-UWB”) or multi-band OFDM UWB while the physical layer of the UWB Forum is based on direct sequence UWB (“DS-UWB”). The major difference between MBOA-UWB and DS-UWB is that MBOA-UWB splits the entire UWB spectrum into several bands during which orthogonal frequency division multiplexing (“OFDM”) is used.
In addition to these physical layer differences, the MAC layer is also different for these competing UWB technologies. The WiMedia MAC, as defined in ECMA-368 [1], consists of both CSMA/CA in the prioritized contention access (“PCA”) period and time division multiple access (“TDMA”) in the contention free period. A superframe in the MAC defined by the UWB Forum, as specified in IEEE 802.15.3 [2], consists of a contention access period (“CAP”) and channel time allocation period (“CTAP”). In CAP, CSMA/CA is used, while slotted Aloha and TDMA are used in the CTAP.
Another major difference in the MAC of these two proposals lies in the formation of their respective network topologies. Under the IEEE 802.15.3 approach, nodes within communication range of each other are organized into a piconet, which is managed under a piconet coordinator (“PNC”). The disadvantage of this approach is that no specification is available for multi-hop networks.
In contrast, under the WiMedia approach, nodes using the same beacon period (“BP”) are organized into a single distributed peer-to-peer network and the WiMedia MAC uses a fully distributed protocol with no central point of control or coordinator. When two networks with different BPs come within range of each other, merging of the BPs is necessary. Once this is done, the individual peer-to-peer networks become a multi-hop distributed network.
Although both the IEEE 802.15.3 MAC and the WiMedia MAC can be extended to support multi-hop wireless networking among devices, the performance of these types of multi-hop networks is not scalable and fails to achieve some of the primary goals of wireless mesh networking.
Specifically, under the IEEE 802.15.3 MAC approach, there is no solution for internetworking of piconets. Thus, the IEEE 802.15.3 completely fails to describe how a mesh network can be formed from piconets. As a result, no multi-hop performance information is provided either.
Additionally, under the IEEE 802.15.3 MAC approach, no resource allocation for a mesh network is even contemplated. The described allocation scheme for piconet is not applicable to a multi-hop mesh network.
Finally, under the IEEE 802.15.3 MAC approach, an individual piconet is under centralized control of the PNC. One significant drawback of this scheme is that when a network size is large, this scheme is not scalable and easily fails. Although the centralized control of the PNC can be passed from one node to another, such passing causes a significant amount of overhead and proves to be too slow to meet the requirements of high speed networking.
Under the WiMedia MAC approach, a mesh network is formed by merging different groups of peer-to-peer networks with different BPs. However, resource allocation between groups being merged can be in conflict. The resulting requirement of resolving such conflicts also proves to be too slow and non-convergent.
Additionally, under the WiMedia MAC approach, distributed resource allocation is only carried out locally and no end-to-end resource allocation solution is contemplated. As a result, there is a significant increase in communication errors because the routing protocol may unknowingly select a routing path without enough resources. Therefore, what is needed is a system and method that overcomes these significant problems found in the conventional systems as described above.